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4EAT Paddle shifters

This is about my paddle shifter project on my GL-10 with the 4EAT automatic. I used a 1990 Legacy TCU because it was easier to modify the code, it uses a much faster 68HC11 processor vs the stock GL-10 TCU which is an old Hitachi type.

The first thing was to graft the Legacy TCU onto the GL-10 harness. It's quite straightforward - I basically matched up the wires using the wiring diagrams. There are a few differences, like the "1 hold" switch, but these things aren't needed once the paddle shift is in place. The Legacy also uses a atmospheric sensor input which I left disconnected. The tach input to the Legacy TCU is 0-5V where as the GL-10 TCU is right off the coil. I initially hooked it straight up and it worked, however I wasn't really happy with it so I used a zener diode and a resistor to clip the signal.

Apparantly the Legacy 4EAT has a stronger high clutch, as initially the 2-3 shift was pretty slow. The transfer clutch has changed as well. To resolve the 2-3 shift problem, I modified the maps in the TCU ROM to make the 2-3 shift faster. This solved that problem.

Initially I modified the maps for the transfer clutch; this made the AWD work again, but it wasn't so great. Sure, it worked as well as it did with the GL-10 TCU but there was a lot of room for improvement. There was a delay in engagement, and it sometimes spun the front tires on takeoff. I decided to upgrade the Duty C solenoid/valve body in my 4EAT to a Legacy unit, along with the orifice plate right behind the Duty C valve body. There were obvious differences in these parts, it seems like it is designed to flow much more fluid volume to the transfer clutch unit. I also replaced the friction discs while I was in there. It's a tad grabby now, but it works much better; I'm back to using the original Legacy TCU transfer clutch maps in place. I'm sure the clutch plates just need to break in a bit, as the cluch was pretty tight when I put it back together.

The TCU was modified by soldering a socket onto the circuit board. I was going to use a different Legacy TCU but it had no holes to solder the socket! I'm not sure what year that TCU was. After the socket is in place, there is a 0-ohm resistor on the bottom of the board that needs to be moved to enable the new socket. The ROM chip I am using is a SST27SF512; this EEPROM is easily reprogrammed without a UV eraser.

The paddles are just bent metal rods that I tack welded to some switches. They work pretty good. I made a small metal frame that attached to the steering column; the switches screw down into that. The paddles use the "manual" and "power" button inputs to the TCU. The paddle code will protect against overrev on downshift, upshift at redline, and downshift to 1st when stopped.

My most recent modification is a DCCD knob. It's a six position rotary switch with FWD, 75%, 100%, 150%, 200%, 4WD settings. It still allows the TCU to calculate the transfer clutch value but it then it modifies it depending on the knob setting; 100% would be stock, 200% would be twice as aggressive as stock, etc. The DCCD knob switch has some 1N4001 diodes wired in series between each pole. The FWD switch pole is attached to ground and the common is attached to the atmospheric sensor input. FWD=0V, 75%=0.5V, 100%=1V, 150%=1.5V, 200%=2V, 4WD=2.5V. If the switch is disconnected the code defaults to 100%.

I'd like to know more about modifying the TCU as i will be putting an early legacy 4sp auto in my 83 leone sedan in the near future.

Is it possible to modify the shift points and the aggressiveness of the gear changes? I really wanna learn more.

How exactly did you hack it?

Yes, it's possible to modify the shift points, torque converter lockup, line pressure, transfer clutch, etc. Phil over at www.alcyone.org.uk has been doing some work with SVX TCUs, which are similar to the Legacy ones. I used his tcuscan software to interface to the select monitor port on the Legacy TCU. The tcuscan software had all the wrong memory locations though, so I had to figure this out; while the Legacy and the SVX TCUs use the same type microprocessor, the circuit board and the ROM are similar but not the same.

To hack it I downloaded the ROM through the select monitor interface. I then used IDA Pro software to disassemble the ROM to the assembly source code. This is the lengthy part, where I had to figure out what the code meant and what it was doing.

Once I figured out where to hook into the code, I made my paddle and dccd assembly code and compiled it. I then used a hex editor to modify the ROM file so that it would execute my code before it executed the original code. I stuck my code in some unused ROM locations.

Then, the ROM file was burned into a chip and stuck on the TCU. Okay, it wasn't that simple, more like crash and burn. But after a while I got it to work and with some more trial and error the paddle and dccd was working just the way I wanted.

i think it should be mentioned that this is an extremely intense project, beyond the means of most folks. i like that you had to do some welding and assembly code to do this, that's great!

probably one of the most technical and difficult projects ever posted on here. not many people have the skill or time to put into something that in depth on the software side (particularly here). others have done it, but they're usually unwilling to talk about it.

i think it should be mentioned that this is an extremely intense project, beyond the means of most folks. i like that you had to do some welding and assembly code to do this, that's great!

probably one of the most technical and difficult projects ever posted on here. not many people have the skill or time to put into something that in depth on the software side (particularly here). others have done it, but they're usually unwilling to talk about it.

Thanks Gary, this is my first time modding any ROM on a car but I'm pretty good at this kind of stuff. I used to do the hardware/software for motion control, servo loops, that kind of stuff.

About 6 months back I quit my job because I was about to have knee surgery and I hated who I worked for; that gave me some time to tinker with stuff. I have a job again but just doing computer repair, it pays the bills for now. I'm thinking of moving to Canada soon but this isn't the best time of year. My citizenship has been approved and I should get my certificate any day now.

sweetness, what did you do previously? with those skill sets i can't imagine it would be that hard to get a job....if you're willing to relocate of course.

moving to Canada, oh man is that a huge move! what prompted that?

the EA82T ECU can be reprogrammed. i mean really ANYTHING can be done if you have the resources. it might cost $32,000 but it can be done. years ago there used to be a company that did modify EA/ER ECU's. i actually talked to them a really long time ago but don't recall anything about them. though it seems they were out of Australia.

actually there might even be some info on the subaruxt boards about that. someone was playing with the EA chips not too long ago i believe.

If you get serious about this, I could email you my ROM file, although you'd need an EEPROM burner. You'd need up upgrade your transfer clutch if it's the same as mine was.

Yes, it's currently set up to enable/disable paddle mode by pulling both paddles at once. Once out of paddle mode it works automatic just like before.

I will probably take you up on that offer eventually. but no way am I delving into anything this serious until the loyale has it's new motor and the 4runner is back on the road (so not until summer sometime, most likely).

I think you've hit the nail on the head with what you've done. full auto shifting, as well as full manual (I'm assuming when you're using the paddles, it doesn't downshift on it's own like it does with the stock selecters). and the DCCD knob is genious!!

did you make the DCCD knob, or use an STi one?

replacing/upgrading the transfer clutches will probably happen next summer, regardless. as there's quite a bit of slip right now.

sweetness, what did you do previously? with those skill sets i can't imagine it would be that hard to get a job....if you're willing to relocate of course.

moving to Canada, oh man is that a huge move! what prompted that?

I was an EE for a company that made automated measuring machines. It was a crappy place, I'm much happier now that I'm not there any more. Canada has less people, beautiful scenery, and lots of outdoor stuff to do; perfect for me. I'm done with the "rat race," it's not worth it.

I'm checking out Vancouver Island, and I've been up there twice. Lately I've been looking for jobs and there aren't many. Maybe I'll go back to school.

did you make the DCCD knob, or use an STi one?

My DCCD control is this switch; a few dollars from the surplus store:6327_1.jpg22.58K41 downloads

I still need to make a decal with the switch settings. Maybe an Avery label printed on color inkjet would look good. A quick spray of matte clear coat to finish it off.

so, I've been thinking about doing this for the last few days, and a problem occurred to me....My XT6 (being a 6-cyl) will have a different rpm signal calibration. so the legacy TCU would not work properly.

any chance this would work with an SVX TCU? I know an SVX TCU can control a legacy 4EAT....and I happen to know someone parting out an SVX....so getting my hands on the TCU and plugs would be quite easy.

so, I've been thinking about doing this for the last few days, and a problem occurred to me....My XT6 (being a 6-cyl) will have a different rpm signal calibration. so the legacy TCU would not work properly.

any chance this would work with an SVX TCU? I know an SVX TCU can control a legacy 4EAT....and I happen to know someone parting out an SVX....so getting my hands on the TCU and plugs would be quite easy.

Hmm, yes you are right. I'm sure it's possible to modify the /4 to /6 in a Legacy TCU. OTOH I don't see any reason why a SVX TCU would not work. There are some SVX ROMs on the www.alcyone.org.uk site, so you wouldn't necessarily need to download your TCU ROM through the select monitor.

It would be worthwile to investigate the XT6 4EAT vs a SVX 4EAT to see if the number of clutch discs is similar, etc. Differences could be worked out by modifying the maps but it adds more work, of course.

I know an EA bellhousing can be put an on EJ 4EAT (Gloyale did it). but I'm mostly concerned about the 4-cyl TCU + 6-cyl relationship.

I've been hunting around on subaruxt.com and subaru-svx. as well as that alcyones site that presslabs linked to (HO-LY-CRAP!!!!).

I think what I'm going to do, is wire EJ TCU plugs (I've got at least 2 sets at my house from harnesses I've stripped). in the XT6 in addition to the existing plugs. This way I can try a few different TCUs and see which matches the shift points of the XT6 best. And, if I find one that works well, then I can start modifying code, plug it in, drive it around the block, and if it doesn't work well, plug the ER27 TCU in there, and drive it to work.

I think what I'm going to do, is wire EJ TCU plugs (I've got at least 2 sets at my house from harnesses I've stripped). in the XT6 in addition to the existing plugs. This way I can try a few different TCUs and see which matches the shift points of the XT6 best. And, if I find one that works well, then I can start modifying code, plug it in, drive it around the block, and if it doesn't work well, plug the ER27 TCU in there, and drive it to work.

The two plugs sound like a great idea! Did you mean EG33 (SVX) TCU plugs?

I've been looking into the ROM on how the TCU gets the engine RPM. I'm nearly certain I found it. On the Legacy $C00B = 4. On the SVX $C00B = 6. This number is used to determine how many times the RPM interrupt service routine is called before calculating the engine RPM; essentially a divisor. So it looks like it's as easy as changing one byte in the Legacy ROM.

With a 6 cyl engine on the EJ TCU the most noticable thing would be the forced shift at "redline" which would be too low. Also the engine RPM is used for TC lockup and Duty Solenoid A & C calcs.

The two plugs sound like a great idea! Did you mean EG33 (SVX) TCU plugs?

I've been looking into the ROM on how the TCU gets the engine RPM. I'm nearly certain I found it. On the Legacy $C00B = 4. On the SVX $C00B = 6. This number is used to determine how many times the RPM interrupt service routine is called before calculating the engine RPM; essentially a divisor. So it looks like it's as easy as changing one byte in the Legacy ROM.

With a 6 cyl engine on the EJ TCU the most noticable thing would be the forced shift at "redline" which would be too low. Also the engine RPM is used for TC lockup and Duty Solenoid A & C calcs.

from what I remember (don't have anything in front of me, but have worked on many of both harnesses), the EG33 and EJ TCU plugs are the same. so swapping between those TCUs would be easy. if not, getting my hands on the plugs will be quite easy, so 3 sets of plugs would also be doable

although, if the rpm signal is just the one byte. it might not matter!

and yes, I've been reading up on things, since the shift points themselves are determined based on TPS signal, and speed, for the most part, it wouldn't matter. except when you do romp on it a bit, it'll think it's hit redline a third earlier.

I also want to dig through some FSMs, and compare gear ratios, otherwise when the TCU compares the speed to what gear it should be in, things will work out. (my buddy had that problem when he put a jdm wrx 4EAT in his impreza LX. it worked fine, except the gear ratios were all off, and then when he put the jdm TCU in there, it was expecting a 7k redline, but the ECU would only allow 6200.)

that sounds like a great way to attack this chux, good luck!

i guess my thinking is that if an XT6 TCU ran an EJ transmission, then opposite should work as well?

yea, it's a plan....I'll try to document things as best I can. might even contribute on the alcyone boards, even though most of that is over my head.

Perfect logic, only problem is, that rpm signal. the TCU (as mentioned above) uses rpm for a couple things, and if the TCU is looking for the rpm signal from a 4-cyl, but getting it from a 6, it'll be thrown off. ever seen an EG33 swap hooked up to the stock tach? it'll bury long before it actually hits redline. but again, if that's just one byte that needs to be changed to adjust how it calculates the rpm, than that's easy.